tangential update on this build: i'm cleaning up the megabosses now, and I unintentionally discovered the second or third-easiest method for clearing dorudugan (the first-easiest is definitely scordeo's + bleeding axe modal, there are some BDD-related shenanigans that may or may not be easier depending on how you define "easy").
this build has so much accuracy thanks to the maxed perception and helm of the white void (and extra hit->crit), that with some modest buffing and debuffing, you have an extremely high hit rate with Embrace the Earth Talon on Dorudugan. You need body blows modal (-25 fort), a dedicated chant with just "the long night's..." (-14 fort), devotions (+10 acc), holding onto keeper of the flame (+4 acc from aura), intuitive (watcher's ability), potion of perfect aim, +4 bonus PL (stone of power, potion of ascension, acute/brilliant) on top of hte base gear (helm of the white void and gloves of accuracy, i also recommend switching out ring of focused flame for kuaro's prize for the bonus perception). all easily do-able for a level 20 party. the problem is that dorudugan has a gigantic resolve (max 35) so anything you land lasts for but a blip, and improving your duration via intellect and PL is minimally effective due to inversions. the trick is to reduce dorudugan's resolve instead.
wizard (in my case aloth): knows gaze of the adragan, arkemy'rs wondrous torment. set up an AI script to just spam them whenever they are availble.
this theurge: set up an AI script to just spam embrace the earth talon and ben fidel's.
priest (in my case xoti): knows spark the souls of the righteous. set up an AI script to spam salvation of time if they have an intellect inspiration.
some random other party member with weyc's robe. i used two party members with morningstars for redundancy.
at start of combat, drink all your potions and set up your buffs, and start empowering an ability to trigger weyc's robe's brilliant. in the mean time, your wizard should be manually spamming arkemyr's wondrous torment (or miasma of dull-mindedness), optionally helped along by an empower or a club modal. eventually one will land (mine landed on the first try at ~30% hit rate with no club modal), and thereafter all future attempts will land very easily due to a vanishingly low will from the debuff [especially with a club modal mixed in].
after everyone gets brilliant, have your priest cast spark the souls of the righteous and move everyone into melee range of dorudugan, make sure the morningstar modals are on. have this theurge use the shield cracks until it lands.
after that, it's autopilot. your wizard's AI script will keep refreshing arkemyr's wondrous torment, while your theurge will keep using embrace the erath talon and ben fidel's. earth talon normally despite all the intellect and PL under all these circumstances lasts only 2.9s or so against dorudugan's massive resolve, but with arkemry's wondrous torment in place will instead last ~9s or so, and will have an exceedingly high hit rate. your wizard will have a lower hit rate with gaze of the adragan but they are just there as backup. the shield cracks will make spark the souls of the righteous do tons of damage easily, which will also keep refreshing shield cracks.
i almost could've AFKed at that point, but i stuck around to manually force the theurge to use ben fidel's or embrace the earth talon in situations where i thought one was more important than the other. dorudugan died very quickly (well, by dorudugan standards) and it never got off any of its special attacks. it got about two or three melee attacks in at the beginning and never acted again after that. i occasionally had eder (in my party also) use mule kick as a safety measure, but it was never actually necessary.
this dorudugan clear isn't specific to this build (all the components can be done piecemeal in other ways), but it was a nice unintended discovery from running with this build. and i don't mean to over-sell this build in particular - just as important as having a high-accuracy petrify effect+shield cracks+ben fidel+long night's chant was also arkemyr's wondrous torment and spark the souls.
edit: (meanwhile belranga was a dream scenario for this build, to the point i had to hold back a bit because my first attempt the game crashed because there were too many wicked briars going at the same time; once about ~40 spiders died belranga basically stopped being capable of doing anything due to constant interrupts)